Electric fuse



T. W. KIRKMAN ELECTRIC FUSE Nov. 20, 1934.

mm .Mm

Original Filed Oct. 24, 1930 Gttorneg5 Patented Nov. 20, 1934 UNTED STATE@ PATENT ifi Application October 24, 1930, Serial No. 491,015 Renewed January 10, 1933 17 Claims.

The present invention relates to electrical fuses and particularly to renewable cartridge fuses.

The primary object of the invention is improvement oi the means for venting and cooling the gases generated when the fuse blows. The proposed venting and cooling means are designed not only to permit escape of the gases, but to accomplish this without the emission of any flash or flame; also, to cool the gases sufficiently and to vent them so as to preclude freezing together of the fuse parts.

The features referred to are applicable to the various types of fuses, but more particularly to the ferrule type. Heretofore, end washers have been used in this type of fuse, and the various methods of ventilation have been such as to cause freezing of certain of the parts when the fuse blows. The present mode of Ventilating is particularly advantageous in the ferrule type fuse, because it not only provides for adequate venting of the gases, but also reduces the numy ber of loose parts, since the end washers are eliminated.

Several practical embodiments of the invention, applied to different types of fuses, are shown in the accompanying drawing, wherein,

Fig. 1 is a longitudinal section of a ferrule type of fuse embodying the invention;

Fig. 2, a section on line 2--2 of Fig. 1, showing the venting grooves in one of the inner bushings;

Fig. 3, a fragmentary view of the inner end of one of the grooved bushings as it appears removed from the fiber casing and assembled with the corresponding link holding member, the parts being enlarged to show clearly the location of the venting grooves;

Fig. 4, a perspective of one of the grooved bushings of 1;

Fig. 5, a longitudinal section of a knife blade type fuse to which my invention has been applied;

Fig. 6, a similar View of a modified form of knife blade fuse embodying the invention, the fusible link and link holder assembly being omitted;

Fig. 7, a view similar to Fig. 3, showing a modification of the venting means; and

Fig. 8, a perspective of a modiedform of the link holding member of Fig. 1.

The preferred form of the invention is the ferrule type fuse of Fig. 1, although the venting scheme is equally well adapted to other types of fuses. kThis is illustrated by the knife blade fuse structures of Figs. 5 and 6.

The ferrule type fuse will be described first.

(Cl. 20D- 131) As appears from Figs. 1, 2, 3, and 4, this fuse comprises a ber body or casing 1, the ends of which are enlarged internally and the surfaces threaded so as to receive the externally and internally threaded ferrules or bushings 2, 2. These bushings are identical in. form and, in addition to being threaded on their inner surfaces, are also provided cn said surfaces with a series of longitudinally extending grooves 3. These are the venting grooves, the functioning of which will be described later. Preferably, the grooves 3 are V-shaped in cross section, but they may be given any other suitable form.

Bushings 2, 2 are rmly secured in insulation casing 1 and ordinarily are not intended to be removed. Hence, in claiming certain features of the present invention hereinafter, the term casing is intended to include not only the insulation casing proper, but also these bushings or at least one of them.

As appears from Figs. 3 and 4, the venting grooves 3 are of such depth that they extend somewhat below the bottoms of the threads in the bushings 2, 2. However, in certain cases the grooves may be cut the same depth as the bottoms of these threads, as is shown in Fig. 7. This will be explained hereinafter.

At each end of the casing 1, there is provided a metal link holding member 4 having a reduced inner end 5 and a shoulder 6. The reduced portion 5 is externally threaded and screws into the internally threaded bushing 2, as appears in Fig. 1. Obviously these parts, if desired, may be joined by other than a threaded connection.

The body of member 4 also is externally threaded and the outer end of the member is provided with a flat-sided slot 7. One end of the fusible element or link 8 projects through the slot '7 and is bent over into contact with the outer face of member 4. The bent end 9 of the link is clamped firmly against link holding member 4 by means of an end cap 10. This cap is threaded internally for engagement with the outer threaded surface of the link holding member 4, as appears in Fig. l.

The lower portion of the skirt l1 of cap 10 is unthreaded on its inner surface and is enlarged internally so as to provide a gas venting space 12 between it and the casing 1. In addition, the threading on the bushing 2 and link holding member 4 is arranged so that, when these parts are screwed into place, there is left an annular venting space 13 between shoulder 6 of member 4 and the end of the ber casing 1. This is accomplished ordinarily by not extending the thread on reduced portion 5 all the way up to shoulder 6. Hence, member 4- may be screwed tightly into bushing 2, but not suilcient to bring shoulder 6 against the adjoining ends oi' bushing 2 and casing 1. It will also be noted from Fig. 1 that the construction and arrangement of the parts are identical at both ends or this type of fuse.

1n the construction described, there is provided by means of the grooves 3, 3, a series of gas venting passages leading from the interior of the casing 1 between the link holding member 4 and bushing 2, which connects with the annular passage 13. This passage is open to the space 12, and the latter connects with the atmosphere. Consequently, when the fuse blows, a large part of the gases generated as a result of the melting of link 8 readily escapes through these passages to the atmosphere. At the same time, the venting passages are of such character that adequate 'metal surfaces are provided which serve to cool the gases during their movement through the passages to prevent emission oi any flash or flame from the fuse. Likewise, this cooling ci the gases prevents fusing or" the parts together, so that the caps can be removed readily. Some ventilation is obtained also by the gases passing through the link opening 7 in member Il, between the connecting threads on this member and cap 10, and thence to the atmosphere through annular passage 12. Ventilation along this path, however,

. is reduced to a minimum by the provision of vent grooves 3, 3 which serve to exhaust the bulk of the gases to the atmosphere and thereby greatly lessen the likelihood` oi end cap 10 freezing in place.

While the bulk o gases with the described venting arrangement passes between two threaded members, viz., bushing 2 and member 4, the presence of the venting grooves 3,3 prevents the depositing of metal upon the threads which would result in these members freezing together.

As stated, venting grooves 3, 3 preferably are made deeper than the threads in bushing 2.

However, it is possible for these grooves to uction properly as venting means for the fuse, even tho-ugh they are cut the same depth as the threads. This is illustrated in Fig. 7. Since the interengaging threads on bushing 2 and link holding member 4 must be of slightly different diameters, there is always a slight clearance between the male threads on one of the niembers and the iemalethreads on the other. r1`his is shown at 14 in Fig. 7.v as a result, even with the venting grooves 3 of the same depth as the threads, longitudinal venting passages are provided between members 2 and e, as indicated at 15 in Fig. 7. 1t is obvious that the capacity of the venting grooves 3 may be varied by either changing the size of the grooves or the fit of the threads, or both. f

Figs. 5 and 6 show the Ventilating scheme applied to a knife blade fuse. rZlhe constructions of these two iigures are the same, except in Fig. 5 the ferrule or bushing 2 is threaded onto the outside of the liber casing 1, while in Fig. 6 it is threaded into the nber casing, similarly to the ierrule type construction of Fig. 1. No-V claim is made herein tothe particular type of knife blade fuse shown, since this is covered by my application Serial Number 116,671, filed June 17, 1926 (now Patent No. 1,928,997, dated October 3, 1933).

In the form of knife blade fuse shown in Fig. 5, each end of the liber casing `1 is reduced in size to form a shoulder 16. rlhe reduced portion 17 of the casing is externally threaded to receive the ferrule or bushing 2 which is threaded on both its inner and outer surfaces. Reduced portion 17 is not threaded close up to shoulder 16, thereby providing for spacing ci the end of bushing 2 from the shoulder to peri; it venting at this point. The outer threaded lsurface of ferrule 2 is provided with a series of longitudinally extending grooves similar to those provided in the bushing of the ferrule type lfuse. The upper or permanently closed end ci the fuse is provided u'th a cap 18, the skirt of which is internally threaded for engagement with ferrule 2, as appears in Fig. 5. The threading does not extend all the way to the inner end of the skirt, thereby permitting the cap to bey screwed down tightly and yet leave a venting space between it and the adjoining ends of bushing 2 and casing 1. For the same reasons, the skirt of cap 18 is of such length as to space its lower end from shoulder 16 of the casing, when the cap is in place.

At the lower end of the fuse, which is adapted to be opened for the purpose of renewing the fusible element 8, there is an outer errule 19 which is threaded onto ferrule 2. Ferrule 19 is threaded similarly to cap 18, so as to provide the necessary venting space between it and the ends of casing 1 and ferrule 2. Likewise, the ferrule is of proper Width to leave the desired venting space between the inner end of the ferrule and shoulder 16 of the casing. Swiveled on ferrule 19 isa ring 20. Removal `of ring 20 from ferrule 19 is prevented by coacting flanges 21, 22, provided on these parts. At the same time, ring 29 may be slid lengthwise on ierrule 19 for a purpose to be explained later. 1

Fuse element 8 forms part cfa fuse element assembly which is adapted to be placed in casing 1 or removed therefrom, as a unit. In general, this assembly includes, in addition to link 8, ber reinforcing bar 23, knife blade terminals 24, 2&1, spacing members 25, 25, end 26, and connecting members 27, 27. When this assembly is in place, as shown in Fig. 5, the upper knife blade 2d projects through a slot 18 in cap 18. At the Ylower end of the fuse, the assembly is held in the casing by reason of the threaded engagement between the swiveled ring 2G and disk 26.

When the fuse blows, the gases escape at the top of the fuse by passing, as indicated by the arrows, between cap 18 and the end of casing 1, and thence through venting passages 3 to the atmosphere. At the lower end of the fuse the escape of the gases principally is between ferrule 19 and the end of casing 1, and thence through venting passages 3 to the atmosphere.

Fig. 5 shows a modified form oi knife blade fuse in which the grooved bushings are threaded into the ber casing 1. `In thisiigure, the fuse link and the fuse link assembly have been omitted for the sake of clearance. 1n this construction, the upper cap 28 hasa reduced portion 29. This reduced portion is threaded externally for engagement with the inner threaded surface of the bushing 2 which is located vin the end of the nber casing.

At its lower end the fuse is constructed in the same manner as is that of 5, except that the bushing 2'is threaded into the fiber casing 1 and,4 venting grooves 3 are on the inner surface of the within the ends of casing 1 is not extended to shoulder 16, nor do the threads on cap 28 and ferrule 19 extend all the way to the inner ends of the reduced portions of these members. Thus, as in the construction of Fig. 5, suitable venting spaces are provided between these members and the ends and shoulders 16 of casing 1.

With this construction, and arrangement of the parts, escape of the gases at the upper part of the fuse, as indicated by the arrows, is between cap 28 and bushing 2 by means of venting grooves 3, and thence to the atmosphere. At the lower end of the fuse, the gases escape principally by means of venting grooves 3, whence they pass between ferrule 19, ring 20, and the end of casing l to the atmosphere.

Although it has been found more practical to locate the venting grooves 3 in the bushings 2, 2, it is possible to obtain efficient results by locating these grooves in the link holding member 4 in the ferrule type fuse, or in the corresponding members 18, 28, and 19 in the knife blade type. In Fig. 8, one of the link holding members 4 of Fig. l is `shown with its reduced portion 5 provided wth a series of venting grooves 3. Obviously, the functioning oi grooves 3 to vent the fuse and the relationship of these grooves to the adjoining threads will be the same, irrespective of the member on which the grooves are located.

Obviously numerous changes may be made in the constructions of the fuses shown and described herein without departing from the inventon, except as the same may be limited by the appended claims.

What is claimed is:

1. In an electrical fuse, the combination of an insulating casing; a metallic ferrule secured within one end of said casing; a link carrying member, said ferrule and said link carrying member being arranged in telescoping relation with a gas venting `space therebetween connecting the interior of the casing with the atmosphere; and a cap mounted on the link carrying member.

2. In an electrical fuse, the combination of an insulation casing; a metallic ferrule threaded into one end of said casing; a link holding member threaded into said ferrule, a gas venting passage being provided between the ferrule and the link holding member, said passage connecting the interior of the casing to the atmosphere; and a cap threaded on said link holding member.

3. In an electrical fuse, the combination of a casing; a metallic fer-rule member carried by one end of said casing; and a link holding member, said ferrule member and said link holding membei' being threaded one within the other, one of said members being provided with a gas venting groove extending yacross its threads and connecting the interior of said casing to the atmosphe-re.

4. The combination in an electrical fuse of an insulation casing; a bushing threaded into one end thereof, said bushing having its internal surface threaded throughout its length and provided with 1a series of longitudinal grooves; an end member having a reduced externally threaded portion located within the bushing and a shoulder spaced from the end of the casing, the body of the end member being threaded; and a cap mounted on the end member.

5. In an electrical fuse, .the combination of an insulation casing; `a ferrule carried by one end thereof, said ferrule being threaded -on one surface throughout its length and provided with a series of longitudinal grooves extending across `and of the same depth as said threads, said f grooves connecting the interior of the casing with the atmosphere; and an end member having threaded engagement with said ferrule.

6. In an electrical fuse, the combination of an insulation casing; a ferrule carried by one end thereof, said ferrule being threaded on one surface throughout its length and provided with a series of longitudinal grooves extending across and of greater depth than said threads, said grooves connecting the interior oi the casing with the atmosphere; and an end member having threaded engagement with said errule.

7. In an electrical fuse, the combination of a casing; a ferrule having threaded engagement with one end thereof, the outer surface of said ferrule being threaded 'throughout its length and provided with a series of gas venting grooves connecting the interior of the casing with the atmosphere; and an end cap internally threaded for engagement with said ferrule.

8. The combination in a fuse of a fiber casing; a ferrule carried by one end thereof, the inner surface of said ferrule being threaded throughout its length; an end member having a reduced portion threaded for engagement with said threaded portion oi the ferrule and provided with a gas venting groove extending across its threads and connecting the interior of the casing with the atmosphere.

9. In a renewable fuse, the combination of a liber casing; a metallic -bushing secured within one end of said casing; and an end member carried by and mounted in said bushing in extended telescoping relation therewith so las to provide an elongated gas venting space between the bushing and the end member leading from the interior of said casing to the atmosphere.

r10. In a renewable fuse, a fiber casing; a metallic bushing threaded within the end of said casing, said bushing havin-g its internal surface threaded throughout its length and provided with a series of longitudinal grooves connecting the interior of the casing with the atmosphere; a metallic end 4member having la portion, externally threaded substantially throughout its length, adapted to seat within and engage the threads Ain said bushing `and having a shouldered portion spaced from the casing, said shouldered portion being externally threaded substantially lthroughout its length; and a metallic cap interiorly threaded for engagement with the end member and having its skirt extending over the casing.

11. In an electrical fuse, the combination of an insulation casing; a metallic ferrule member secured within one end of said casing; a link provide a series of venting passages between said '1 members connecting the interior of the casing with the atmosphere; and a cap mounted on the link carrying member.

12. In a renewable fuse, the combination of a casing; and a link carrying end member havs.

end member having a reduced portion threaded for engagement with said threaded portion of the casing and provided with a series of longitudinai grooves extending across its threads and forming independent gas venting'passages connecting the interior of the casing with the atmosphere, the body of said end member being threaded and provided a shoulder spaced from said end of the casing to form a iiame-denecting surface; and a cap threaded onto the end member.

14. In an electrical fuse, the combination of an insulation casing; a threaded ferrule mounted directly on the insulation casing; and an end member having threaded engagement with said fer-rule, the end member being provided with a plurality of spaced longitudinally disposed grooves extending across its threads and forming a series of independent venting grooves between the ferrule and the end member to connect the interior of the casing to the atmosphere, said ferrule being threaded throughout its length both internally and externally and the end member being adapted to support one end of a fuse link.

15. In a renewable electric fuse, the combination of a casing; a fuse link located therein; and link supporting means at one end of the casing including a pair of telescoping, circumferentially spaced sleeve portions connected together at their outer ends and embracing said end of the casing so as to form a gas venting space between said sleeve portions and the adjacent surfaces of the casing connecting the interior or the casing with the atmosphere, one of said sleeve portions having threaded engagement with said end of the casing.

ll The combination of claim 15 further characterized in that the inner of said pair ofsleeves is in threaded engagement With an internally threaded and longitudinally grooved bushing secured in the end of the casing, said grooves forming independent passages for the escape or" gases from the casing. v

17. The combination in an electric fuse of a casing; a pair of connected cup-shaped end members projecting into the inside and extending over the outside of the casing at each end thereof, one of each pair of said end members having threaded connection with the casing; and a fuse link supported in the casing by the end members, said end members and the adjacent surfaces of the casing being provided with a gas venting space therebetween connecting the interior of the casing with the atmosphere.

' THOMAS W. KRKMAN. 

